Method of recovering tantalum and columbium



METHUD F REQOVERING TANTALUIVI AND COLUMBIUM Donald F. Taylor,Waulregan, Robert L. Baughman, Zion, and Leonard F. Yntema, Wadsworth,11L, assignors to Fansteel Metallurgical Corporation, a corporation ofNew York No Drawing. Application September 6, 1957 Serial No. 632,287

20 Claims. (CI. 75-84) This invention relates to a method of recoveringtantalum and columbium from their ores.

This is a continuation-in-part of United States patent applicationsSerial Numbers 534,610, filed September 15, 1955, now abandoned, and239,393, filed July 30, 1951, now abandoned.

In the case of tantalum or columbium, these metals cannot be recoveredfrom tantalite, columbite and similar ores by a smelting process, norcan they be obtained by a reduction of the oxides with hydrogen. Underthe present process, these ores are fused with caustic soda to convertthe tantalum and columbium into a fused mass of crude sodium tantalateand sodium columbate mixed with a number of impurities. After cooling,the fused mass is crushed and the water soluble impurities removed byleaching with water. The acid soluble impurities are then removed bytreating the mass with hot hydrochloric acid. This converts the sodiumtantalate and sodium columbate into insoluble tantalic and columbicacids. This mixture of acids is then dissolved in hot hydrofluoric acidand potassium carbonate is added to form the double salts, potassiumtantalum fluoride and potass'ium columbium oxyfluoride. The hot solutionis then cooled. The potassium tantalum fluoride crystalizes out leavingthe potassium columbium oxyfiuoride in solution. The columbium salt isthen recovered from the solution.

The pure tantalum and columbium metals may be obtained directly from thedouble fluorides by electrolysis of the respective fused salts. Also,the salts may be converted to oxides by treating the same with analkaline solution such as sodium hydroxide after which the resultingsalt is washed and then treated with an acid such as hydrochloric acidafter which the resulting powder is washed. When tantalum is treatedthis way the resulting oxide is an hydrated oxide (Ta O H O). When thepure tantalum and columbium metals are obtained by electrolysis, themetal become dispersed as fine grains or powder in the salt mass aselectrolysis progresses. After electrolysis, the salt mass is crushedand the metal recovered from the crushed mass.

The electrolysis of the fused tantalum or columbium metal salts is acostly operation. Recovery of the tantalum or columbium metal from theoxides thereof is also a costly operation. The new method of thisinvention provides a more economical means for the production oftantalum and columbium and eliminates many of the costly stepsheretofore used in recovering the metals from the salts or oxides.

V In our co-pending United States patent application, Serial Number534,609, filed September 15, 1955, now abandoned, which is acontinuation-in-part of our United States patent applications, SerialNumber 195,910, filed November 15, 1950, now abandoned, and SerialNumber 239,391, filed July 30, 1951, now abandoned, we have disclosedand claimed a method for the recovery of refracfory metals includingtantalum and columbium whereby the double salt of tantalum or columbium(as for example potassium tantalum fluoride and potassium columbiumoxyfiuoride) is first reacted with aluminum forming an intermetalliccompound or alloy of aluminum and tantalum or columbium. Theintermetallic compound or alloy is reacted with a third metal, such ascopper, silver or gold which is substantially insoluble in the tantalumor columbium, but which alloys with the aluminum. As a result, thetantalum or columbium is obtained in substantially pure form as finelydivided particles dispersed throughout the aluminum-third metal alloy.

We have discovered that tantalum or columbium can be recovered from itscompound by heating the tantalum or columbium compound with an alloy ofaluminum and a third metal, such as copper, silver or gold, which is substantially insoluble in tantalum or columbium. The resulting mixtureincludes columbium or tantalum dispersed therethrough in a finelydivided, substantially pure state. The substantially pure tantalum orcolumbium is then separated from the mixture.

To simplify the description of the new method, reference is madespecifically to the preparation of tantalum and columbium from potassiumtantalum fluoride, tantalum oxide, potassium columbium oxyfluoride andcolumbium pentoxide. It is understood that the method is applicable toother compounds of tantalum and columbium.

In reacting, for example, an aluminum-copper alloy with potassiumtantalum fluoride, the potassium tantalum fluoride may be placed in acrucible or other container, and the potassium tantalum fluoride coveredwith a graphite plate. The alloy may be placed on the graphite plate andthe mass covered with a suitable slag material such as sodium chloride.The graphite plate retains the aluminum-copper alloy above the potassiumtantalum fluoride until the alloy becomes molten. This prevents thealloy from settling at the bottom of the crucible before contacting andreacting with the potassium tantalum fluoride. The mass is then heated;the molten aluminumcopper alloy is allowed to contact the potassiumtantalum fluoride; and reaction occurs. The resulting mass may beagitated with a graphite rod or other inert material to insure athorough mixing of the salt and the aluminumcopper alloy.

The mass resulting from the above reaction includes tantalum in a finelydivided, substantially pure state dispersed therethrough as well asaluminum fluoride and potassium fluoride. The fluorides may bevolatilized or may remain as a constituent of the slag, depending uponthe temperature of the mass. The tantalum is recovered from the ingot bydissolving the copper or an alloy of aluminum and copper remaining inthe mass in nitric acid, following which the tantalum is washed free ofacid and dried.

In the event that the equivalent of three mols of potassium tantalumfluoride is reacted with five mols of copper-aluminum alloy, then thereduction of the potassium tantalum fluoride or the reaction of thissalt with the aluminum-copper alloy may be represented by the followingtheoretical equation:

It is readily seen that under such conditions the mixture resulting fromthe reaction between the aluminumcopper alloy and the potassium tantalumfluoride includes aluminum fluoride, potassium fluoride, free copper andsubstantially pure tantalum dispersed as minute grains throughout thebody of the mixture. Since the copper and tantalum are mutuallyinsoluble, the tantalum is readily separable from the mixture, as bydissolving the copper in nitric acid and then washing the tantalum freeof acid.

' In the event'that a smaller proportion of aluminum is used in thereaction, then only some of the tantalum will be recovered and a portionof potassium tantalum fluoride will remain.

To ensureoptimum recovery of tantalum, it is preferred to employ anexcess of the aluminum-third metal alloy. Under such conditions theproduct resulting from the reaction of the aluminum-third metal.(copper, gold or silver) alloy with, for example, potassium tantalum'fiuoride, includes aluminum fluoride, potassium fluoride,aluminum-copper alloy and tantalum metal in a finely divided,substantially pure state dispersed throughout the asoaeea metallicportion. Undersuch' conditions, substantially all 7 of the fluoridesremain as constituents of the slag. Since the tantalum is substantiallyinsoluble in the copper-aluminum alloy, it may be recovered from thereaction mixture by dissolving the alloy in nitric acid, following whichthe tantalum is washed free' of acid and dried.

In recovering the tantalum metal from tantalum oxide, the method issubstantially identical to the method employed when recovering the metalfrom the halide ex- 'cept that a fiuxing agent such as an alkali metalhalide flux is added to the oxide powder.

' The new method of this invention for the recovery of tantalum andcolumbium from their respective compounds may be illustrated by thefollowing specific examples: Example 1 An aluminum-copper alloy wasprepared by melting lfi parts. by weight of aluminum in a crucible,about '50 parts by weight of sodiumchloride being used as a slag toprotect the aluminum from the atmosphere. The aluminum was heated to atemperature of about 1500 C. and about 140 parts by weight of copperadded. a 35 parts by weight of potassium tantalum fluoride salt wereplaced in a graphite crucible and a graphite plate placed over the salt.About 150 parts by weight of the solid aluminum-copper alloy wereplacedon the graphite plate and approximately 50. parts by weight of sodiumchloride placed over. the aluminum-copper alloy to serve as a protectingslag. The mass was then heated to a temperature. of about 1500" C. andthe molten aluminum-copper alloy allowed to. contact the potassiumtantalum fluoride salt. The resulting mass was maintained at atemperature above the melting point of thev alumimum-copper alloy forapproximately 20 minutes after the alloy became. molten to form areaction mixture. During. this period, the mass was agitated with agraphite rod. After cooling, the slag was removed, and the reactionmixture, in the form of an ingot, was treated with dilute nitric acid todissolve the aluminum-copper alloy. The tantalum was then recovered byfiltering the finely divided particles of tantalum from the nitric acidsolution, following which the tantalumparticles were washed with nitricand hydrochloric acids, washed free. of: these acids with water, andthen dried.

Example 2 Tantalum was produced in the same manner as in Example l,except that silver was employed instead of copper in the alloy. Theresults were substantially the same as in Example 1. 7 Example 3Tantalum was prepared in the same manner as'in Example 1, except thatgold was employed instead of copper in the alloy. The results weresubstantially the same as iniExample 1.

Example 4 An aluminum-copper alloy was prepared by melting parts byweight of aluminum in a crucible, about 50 parts byweight of sodiumchloride being used as a slag to protect the aluminum from theatmosphere. The aluminumewas heated to a temperature of about 1500 C;and about 140 parts by weight of copper added.

25 parts by weight of tantalum oxide were placed in a graphite crucibleand a graphite plate placed over the oxide. About 150 parts by weight ofthe solid aluminum-copper alloy were placed on the graphite plate andapproximately 50 parts by weight of sodium fluoride placed over thealuminum-copper alloy to serve as a protecting slag. The mass was thenheated to a temperature or about 1500" C. and the molten aluminum-copperalloy allowed to contact the tantalum oxide. The resulting mass wasmaintained at a temperature above the melting point of thealuminum-copper alloy for approximately 20 minutes after the alloybecame molten to form a reaction mixture. During this period, the masswas agitated with a graphite rod. After cooling, the slag was removed,and the reaction mixture, in the form of an ingot, was treated withdilute nitric acid to dissolve the aluminum-copper alloy. The tantalumwas then recovered by filtering the finely divided particles of,tantalum from the nitric acid solution, following which the tantalumparticles were washed with nitric and hydrochloric acids, washed free ofthese acids with water, and then dried;

Examples 5 Tantalum was produced in the same manner as in Example 4except that silver-was employed instead of copper in the alloy. Theresults were substantially the same as in; Example 4.

Example 6 Example 7 An aluminum-copper alloy was prepared by melting 15parts. by weight of aluminum in a crucible, about 50 parts by weight ofsodium. chloride being used as a slag to protect the aluminum from theatmosphere. The aluminum was heated to a temperatureof about 1560 C. andabout parts by weight. of copper added.

25- parts by' weight of potassium columbium. oxyfluoride salt wereplaced in a graphite crucible and a. graphite plate placed over thesalt. About parts by weight of the solid aluminum-copper alloy wereplaced. on the graphite plate and about 50 parts by weight of sodiumchloride placed over the aluminumrcopper alloy to. serve as a protectingslag. The mass was then heated to a temperature of about 1500 C. and themolten alloy allowed to contact the potassium columbium oxyfiuoride. Theresulting mass was maintained at a temperature above the melting pointof' the aluminum-copper alloy for approximately 20 minutes after thealloy became molten to. form a reaction mixture. During this period themass wasagitated with a, g aphite rod. After cool.- ing, the slagwas'removed and the reaction mixture, in the form of an ingot, treatedwith dilute nitric acid to dissolve the aluminum-copper'alloy. Thecolumbium was then recovered from the solution by filtering the finelydivided particles of columbium from the nitric acid solution, followingwhich the columbium particles were washed with nitric and hydrochloricacids, washed free of these. acids with water, and then dried.

Example 8 Columbium was produced in the same manner as in Example 7,except that silver was employed instead of copper in the alloy. Theresults were substantially the same as in. Example 7.

Example 9 Columbium was produced in the same manner as in Example 7,except that gold was employed instead of copper in' the alloy}. Theresults were substantially the samea'sinExample7'.

Example 10 An aluminum-copper alloy was prepared by melting 15 parts byweight of aluminum in a crucible, about 50 parts by weight of sodiumchloride being used as a slag to protect the aluminum from theatmosphere. The aluminum was heated to a temperature of about 1500 C.and about 140 parts by weight of copper added.

18 parts by weight of columbium oxide were placed in a graphite crucibleand a graphite plate placed over the oxide. About 150 parts by weight ofthe solid aluminum-copper alloy were placed on the graphite plate andabout 50 parts by weight of potassium fluoride placed over thealuminum-copper alloy to serve as at protecting slag. The mass was thenheated to a temperature of about 1500 C. and the molten alloy allowed tocontact the columbium oxide. The resulting mass was main- 'tained at atemperature above the melting point of the Example 11 Columbium wasproduced in the same manner as in Example 10, except that silver wasemployed instead of copper in the alloy. The results were substantiallythe same as in Example 10.

Example 12 Columbium was produced in the same manner as in Example 10,except that gold was employed instead of copper in the alloy. Theresults were substantially the same as in Example 10.

The foregoing detailed description is given for clearness ofunderstanding only, and no unnecessary limitation should be understoodtherefrom, for some modification will be obvious to those skilled in theart.

We claim:

1. In the recovery of a metal selected from the group consisting oftantalum and columbium, the method which comprises: heating an inorganiccompound of the selected metal with an alloy of aluminum including athird metal, said compound being substantially completely reducible tothe metal state in molten aluminum, said third metal being present in asufl'lcient quantity to dissolve substantially all of the aluminum andbeing incapable of dissolving the selected metal and having a lowermelting point than the selected metal, to form a reaction mixtureincluding said selected metal in a finely divided, substantially purestate; and separating the selected metal from the mixture.

2. The method as set forth in claim 1 wherein an excess of an alloy ofaluminum and the third metal is employed.

3. In the recovery of a metal selected from the group consisting oftantalum and columbium, the method which comprises: heating an inorganiccompound of the selected metal with an alloy of aluminum including athird metal, said compound being substantially completely reducible tothe metal state in molten aluminum, said third metal being present in asuflicient quantity to dissolve substantially all of the aluminum andbeing incapable of dissolving the selected metal, to form a reactionmixture including said selected metal in a finely divided, substantiallypure state, said third metal being a member of the class consisting ofcopper, silver and gold; and separating the selected metal from themixture.

4. The method of recovering a metal selected from the group consistingof tantalum and columbium from a double fluoride of an alkali metal andthe selected metal which comprises: heating a double fluoride of analkali metal and the selected metal with an alloy of aluminum includinga suflicient quantity of a third metal to dissolve substantially all ofthe aluminum, said third metal being incapable of dissolving theselected metal and having a lower melting point than the selected metal,to form a reaction mixture including the said selected metal in a finelydivided, substantially pure state; and separating the selected metalfrom the mixture, said double fluoride being substantially completelyreducible to the metal state in molten aluminum.

5. The method as set forth in claim 4 wherein an excess of thealuminum-third metal alloy is employed.

6. The method of recovering a metal selected from the group consistingof tantalum and columbium from" a double fluoride of an alkali metal andthe selected metal, which comprises: heating a double fluoride of analkali metal and the selected metal with an alloy of aluminum includinga sufficient quantity of a third metal to dissolve substantially all ofthe aluminum, said third metal being incapable of dissolving theselected metal, to form a reaction mixture including the said selectedmetal in a finely divided, substantially pure state, said third metalbeing a member of the class consisting of copper, silver and gold; andseparating the selected metal from the mixture, said double fluoridebeing substantially completely reducible to the metal state in moltenaluminum.

7. The method of recovering a metal selected from the group consistingof tantalum and columbium from a double fluoride of an alkali metal andthe selected metal which comprises: heating a double fluoride of analkali metal and the selected metal with an alloy of aluminum includinga suflicient quantity of copper to dissolve substantially all of thealuminum, to form a mixture including the selected metal in a finelydivided, substantially pure state; and separating the selected metal inits pure state from the mixture, said double fluoride beingsubstantially completely reducible to the metal state in moltenaluminum.

8. The method as set forth in claim 7 wherein the selected metal istantalum.

9. The method as set forth in claim 7 wherein the selected metal iscolumbium.

10. The method as set forth in claim 7, wherein the alkali metal ispotassium.

11. The method as set forth in claim 10, wherein the selected metal istantalum.

12. The method as set forth in claim 10, wherein the selected metal iscolumbium.

13. In the recovery of a metal selected from the group consisting oftantalum and columbium, the method which comprises: heating an oxide ofthe selected metal with an alloy of aluminum including a third metal,said third metal being present in a suflicient quantity to dissolvesubstantially all of the aluminum and being incapable of dissolving theselected metal and having a lower melting point than the selected metal,to form a reaction mixture including said selected metal in a finelydivided, substantially pure state; and separating the selected metalfrom the mixture, said oxide being substantially completely reducible tothe metal state in molten aluminum.

14. In the recovery of a metal selected from the group consisting oftantalum and columbium, the method which comprises: heating an oxide ofthe selected metal with an alloy of aluminum including a suflicientquantity of a third metal to dissolve substantially all of the aluminum,said third metal being incapable of dissolving the selected metal, toform a reaction mixture including said selected metal in a finelydivided, substantially pure state, said third metal being a member ofthe class consisting of copper, silver and gold; and separating theselected metal from the mixture said oxide being substantiallycompletely reducible to the metal state in molten aluminum.

l I l aaoasas .15. The method as set :forth 'in claim .13 wherein anexcess of an alloy of aluminum and :the third metal is employed. v

16. The method :as set forth in .claim 13 wherein the selected metal istantalum.

17. The method as set forth in dlaim 13 wherein the selected metal is.columbium.

.18. The method as set forth in .claim 14 wherein the .selected metal istantalum.

119. The method .as set forth in claim 14 wherein the selected metal is.columbium. 20. In the recovery of a metal selected :from the groupconsisting of tantalum and columbium, the method which comprises:melting an inorganic compound of theselected metal, the compound beingsubstantially completely reducible to the metal state in moltenaluminum; adding .an alloy of aluminum including a third metal to themolten compound of theselected metal, said third metal being capable ofdissolving aluminum and present in'a suflicient quantity to dissolvesubstantially all of the aluminum and being incapable of dissolving theselected :metal and having a lower melting point than the selectedmetal, to form a reaction mixture including :said selected .metal in afinely divided, substantially pure state; and separating the selectedmetal from the mixture.

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1. IN THE RECOVERY OF A METAL SELECTED FROM THE GROUP CONSISTING OFTANTALUM AND COLUMBIUM THE METHOD WHICH COMPRISES: HEATING AN INORGANICCOMPOUND OF THE SELECTED METAL WITH AN ALLOY OF ALUMINUM INCLUDUNG ATHIRD METAL, SAID COMPOUND BEING SUBSTANTIALLY COMPLETELY REDUCIBLE TOTHE METAL STATE IN MOLTEN ALUMINUM, SAID THIRD METAL BEING PRESENT IN ASUFFICIENT QUANTITY TO DISSOLVE SUBSTANTIALLY ALL OF THE ALUMINUM ANDBEING INCAPABLE OF DISSOLVING THE SELECTED METAL AND HAVING A LOWERMELTING POINT THAN THE SELECTED METAL, TO FORM A REACTION MIXTUREINCLUDING SAID SELECTED METAL IN A FINELY DIVIDED, SUBSTANTIALLY PURESTATE; AND SEPARATING THE SELECTED METAL FROM THE MIXTURE.